The present invention relates to non-noble metal combustion catalysts for carbon monoxide comprising copper-aluminum/cerium-aluminum complex oxides and aluminum oxide support, their preparation and use in the Fluid Catalytic Cracking process (FCC) of the petroleum industry. More particularly, the present invention relates to non-noble metal combustion catalysts for carbon monoxide comprising copper-aluminum complex oxide uniformly dispersed in cluster form on the Al2O3 support pre-covered with highly dispersed microcrystals of Cexe2x80x94Al complex oxide, a process for their preparation and their use in the FCC process of petroleum refining as carbon monoxide combustion catalysts with high catalytic activity, high hydrothermal stability and the ability to reduce the emission of NOx.
In the FCC process of petroleum refining, the catalysts for catalytic cracking used in a vast amount usually need to be regenerated by the aid of the combustion catalysts for carbon monoxide. The combustion catalysts for carbon monoxide are called carbon monoxide combustion promoters (or promoters for short). Up to now, the combustion catalysts for carbon monoxide wildly used in the art all have noble metals of VIII group, such as Pt, Pd, etc, as their active component. In order to solve the problems of noble metal shortage and high production cost, non-noble metal carbon monoxide combustion catalysts, including perovskite-type complex oxides and non-perovskite type oxides, have been developed to substitute for all or part of noble metal (CN 1022542C and CN 1072109A etc). However, for these non-noble metal catalysts, neither their catalytic activity and stability, nor the reliability and facility of the related process, can be comparable to that achieved by using noble metal catalysts. For instance, the catalysts usually become inactive at the high temperature used in hydrothermal condition due to agglomeration of the active components and inevitable by-products. Therefore, researchers in the art have been making great efforts to improve the performances of the non-noble metal combustion catalysts.
The present inventors have developed two kinds of suitable complex oxides with imperfect structure on the bases of the structural chemistry principles. The interactions between two complex oxides make it possible for the catalytic active component to be uniformly dispersed on and firmly combined with the support, and thereby combustion catalysts for carbon monoxide having good performance and meeting the demands of industry have been prepared, showing a new progress in the art.
Therefore, an object of the present invention is to provide carbon monoxide combustion catalysts comprising metal complex oxides firmly combined with a support as catalytic component, which have high catalytic activity, high hydrothermal stability and the ability to achieve the conversion of CO and HC, and hence can be used to substitute for noble metal combustion catalysts for carbon monoxide. The catalyst of the present invention also has favorable effects in reducing the NOx exhaust and the contamination to the environment. It is also an object of the present invention to provide a process for preparing the non-noble metal combustion catalysts. Another object of the present invention relates to the use of the non-noble metal combustion catalysts as carbon monoxide combustion catalysts in the FFC process. Other objects of the present invention will be embodied in the following detailed description of the present invention.
The present invention relates to non-noble metal combustion catalysts for carbon monoxide comprising cerium-aluminum and copper-aluminum complex oxides successively loaded on aluminum oxide support, wherein the weight ratio between the two loaded complex oxides and the aluminum oxide support is respectively from 0.02 to 0.10, preferably 0.04-0.06 for Cexe2x80x94Al complex oxide and 0.05-0.15, preferably 0.08-0.11 for Cuxe2x80x94Al complex oxide. Preferably, the Cexe2x80x94Al complex oxide covering the surface of the aluminum oxide support is in the form of nanometer microcrystals with an imperfect structure, having a general formula of [Ce1xe2x88x92yAly][O2xe2x88x92y/2xe2x96xa1y/2][I]; and the Cuxe2x80x94Al complex oxide is dispersed in cluster form on the microcrystals of the Cexe2x80x94Al complex oxide covering the aluminum oxide support, having an imperfect structure and a general formula of [Cu1xe2x88x923x/2Alxxe2x96xa1x/2]O [II]; wherein x=0.05-0.23, preferably x=0.10-0.17; and y=0.05-0.30, preferably y=0.10-0.22; xe2x96xa1 presents the vacancy in the crystal structure.
The present invention further relates to a process for preparing the aforesaid catalysts, which comprises:
A. impregnating the aluminum oxide support with an aqueous solution formed by mixing an aqueous solution comprising Cexe2x80x94Al compounds, preferably Ce and Al salts, such as their nitrates, with citric acid or its aqueous solution in a citric acid/total Cexe2x80x94Al metal ions molar ratio of 0.3-1.0, then the impregnated support being baked at 100-140xc2x0 C. for 2-4 hrs, pyrolysated at 200-300xc2x0 C. for 2-3 hrs, and then activated at 600-750xc2x0 C. for 2-5 hrs, to obtain the solid Al2O3 support covered with microcrystals of Cexe2x80x94Al complex oxide; and
B. impregnating the solid obtained in the step A in an aqueous solution formed by mixing an aqueous solution comprising Cuxe2x80x94Al compounds, preferably Cu and Al salts, such as their nitrates, with citric acid or its aqueous solution in a citric/total Cuxe2x80x94Al metal ions molar ratio of 0.3-1.0, then the impregnated solid being baked at 100-150xc2x0 C. for 2-4 hrs, pyrolysated at 200-300xc2x0 C. for 2-3 hrs, and then activated at 500-650xc2x0 C. for 2-3 hrs, to obtain the final catalyst which further comprises Cuxe2x80x94Al complex oxide dispersed on its surface pre-covered with the microcrystals of Cexe2x80x94Al complex oxide.
The present invention also relates to the use of the aforesaid catalysts as carbon monoxide combustion catalyst in FCC process of petroleum refining.